1. Technical Field
The present disclosure relates to a stator core and a permanent magnet motor.
2. Description of the Related Art
A permanent magnet motor generates torque with pulsation in no-load driving. The pulsation of the torque is called coming toque. The cogging torque inhibits smooth rotation of a rotor, resulting in vibration and speed fluctuation of the motor. Therefore, the reduction of cogging torque is important in design of a permanent magnet motor.
Conventionally, in a stator core used for reducing cogging torque of a permanent magnet motor, teeth coupling portions are entirely closed and are not provided with slot openings.
However, when the teeth coupling portions closing the slots are made thick, cogging torque becomes low but torque also decreases.
There has been disclosed a stator core as a technique for reducing cogging torque (see JP-A-2005-80474). The core sheets laminated in the stator core include portions where teeth ire coupled together and portions where the teeth are not coupled, and portions for coupling the teeth are made thinned.
In addition, there has been disclosed a stator having a plurality of laminated core sheets in which teeth coupling portions are made thin and different in angle (see JP-A-2004-304997).
Further, there has been disclosed a stator core having a plurality of laminated core sheets with at least two kinds of teeth tip angles (see JP-A-2003-88078). According to the technique disclosed in JP-A-2003-88078, cogging torque can be reduced.
There has also been disclosed a stator core having laminated core sheets with coupled teeth and core sheets with non-coupled teeth (see JP-Y-61-62537). According to the technique disclosed in JP-Y-61-62537, it is possible to reduce occurrence of short-circuit of magnetic flux produced by a permanent magnet at the teeth coupling portions, thereby suppressing reduction of torque.
Furthermore, there has been disclosed a stator core having three kinds of core sheets laminated in combination such that the teeth coupling portions and the slot openings are alternately arranged in one of the sheets (see Japanese Patent No. 4476202).